SAMPLING FOR PESTICIDE RESIDUES IN CALIFORNIA WELL …
Transcript of SAMPLING FOR PESTICIDE RESIDUES IN CALIFORNIA WELL …
SAMPLING FOR PESTICIDE RESIDUES IN CALIFORNIA WELL WATER
2018 Update
Annual Well Sampling Report Pursuant to the
Pesticide Contamination Prevention Act
California Environmental Protection Agency DEPARTMENT OF PESTICIDE REGULATION
Environmental Monitoring Branch Groundwater Protection Program
November 2019
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Cover photo—old windmill that once pumped groundwater. Photo credit: Coco Parisienne
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SUMMARY
As required under Food and Agricultural Code (FAC) section 13152(e), this report summarizes the results of groundwater sampling for pesticide residues from January through December 2017 by the Department of Pesticide Regulation (DPR) and the State Water Resources Control Board (SWRCB). The report also includes United States Geological Survey (USGS) data from 2011 to 2016 that had not been previously reported to DPR. Actions taken by DPR to prevent migration of pesticides to groundwater from nonpoint agricultural sources are identified in Table 2 and wells with detections are identified by county in Appendix D.1
A total of 5,635 wells were sampled for one or more of 315 agricultural use pesticides and pesticide degradates (Table i). Eighty-six pesticides/degradates were detected; 18 of the detected pesticides are no longer registered for use in California (Table 2).
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Table i. Summary of well sampling results from DPR (2017), SWRCB (2017), and previously unreported USGS data (2011-2016).
DPR SWRCB USGS †TOTALPercent
Detections
‡ Pesticides/Degradates Sampled 49 98 254 315 27.3
Pesticides/Degradates Detected 13 9 81 86
‡‡ Wells Sampled 84 4,567 1,063 5,635 14.0
Wells with Detections 47 354 392 786
Counties Sampled 5 57 51 57 73.7
Counties with Detections 4 19 38 42
† “Total” reflects unique values, not a summation of values. For example, of the 58 California counties, some counties are
sampled by more than one agency, but some are not sampled at all. (For the 2017 data, San Francisco County was not sampled.)
‡ “Pesticides Sampled” and “Pesticides Detected” represents the total number of pesticides sampled or found in
groundwater regardless of the number of sampling events or detections that occurred during the reporting period.
‡‡ “Wells Sampled” and “Wells with Detections” represents the total number of wells sampled or found to contain
pesticide residues regardless of the number of sampling events or detections that occurred during the reporting period.
1 Although DPR is required to provide locations of sampled wells, in this report information is summarized by county to protect well owner privacy. DPR can provide additional location information—including township, range, and section—upon request.
2 Some exceptions to the “agricultural use” status of sampled pesticides apply; some industrial use pesticides and pesticides that are no longer—or never were—registered for use in California are included due to the varying monitoring goals of reporting agencies.
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PREFACE This report fulfills the requirements of the Pesticide Contamination Prevention Act of 1985 (PCPA), Assembly Bill (AB) 2701 of 2004, and Senate Bill 1117 of 2014. The PCPA originally required DPR to submit the results of groundwater sampling for pesticide residues in an annual written report; AB 2701 amended the PCPA to require DPR to post the information on the DPR Web site.
ACKNOWLEDGEMENTSThe authors wish to thank the reviewers whose unique perspectives and experiences helped ensure the accuracy and readability of this report. We gratefully acknowledge the staff of DPR and cooperating federal, state, local, and private agencies for contributing to the database.
DISCLAIMERAs required by the PCPA, this report describes active ingredients of registered pesticide products that have been found in groundwater. DPR provides this information to satisfy legal mandates and provide information to the public. Any discussion of commercially available pesticide products does not constitute an actual or implied endorsement of the products by DPR.
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ABBREVIATIONS
CAC County Agricultural CommissionerCALVUL California Vulnerability Model3CCR Title 3, California Code of RegulationsCDPH California Department of Public HealthDDW Division of Drinking WaterDPR Department of Pesticide RegulationFAC Food and Agriculture CodeGAMA Groundwater Ambient Monitoring and Assessment ProgramGWPA Ground Water Protection AreaGWPL Groundwater Protection ListLLNL Lawrence Livermore National LaboratoryLEACHM Leaching Estimation and Chemistry ModelMCL Maximum Contaminant LevelMCLG Maximum Contaminant Level GoalOEHHA Office of Environmental Health Hazard AssessmentPCPA Pesticide Contamination Prevention ActPHG Public Health GoalPMZ Pesticide Management Zoneppb Parts per billionSNV Specific Numerical ValueSWRCB State Water Resources Control BoardU.S. EPA United States Environmental Protection AgencyUSGS United States Geological Survey
TABLE OF CONTENTS
SUMMARY ........................................................................................................................................ i
PREFACE ........................................................................................................................................... ii
ACKNOWLEDGEMENTS ...................................................................................................................... ii
DISCLAIMER ...................................................................................................................................... ii
ABBREVIATIONS .............................................................................................................................. iii
BACKGROUND ................................................................................................................................. 1PROTECTING GROUNDWATER FROM PESTICIDE CONTAMINATION — THE PCPA ......................................... 1IDENTIFYING POTENTIAL GROUNDWATER CONTAMINANTS UNDER THE PCPA ............................................ 3
Using Environmental Fate Data to Predict Pesticide Behavior in the Environment ................... 3Using Computer Modeling Tools to Predict Pesticide Contamination Potential ........................ 4
MONITORING FOR PESTICIDES—PRIORITIZING THE CANDIDATES .............................................................. 4RESPONDING TO PESTICIDE DETECTIONS IN GROUNDWATER .................................................................... 5
Areas of Non-Authorization ...................................................................................................... 6 ASSESSING THE EFFECTIVENESS OF MITIGATION MEASURES .................................................................... 6
SAMPLING RESULTS .......................................................................................................................... 7DETECTIONS OF PESTICIDES AND RELATED DEGRADATES ............................................................................ 7
DPR RESPONSES TO PESTICIDE DETECTIONS ................................................................................... 37
REFERENCES .................................................................................................................................... 58
APPENDIX A: Ground Water Protection Areas (GWPA) ..................................................................... 59
APPENDIX B: Principal Sampling Agencies......................................................................................... 63
APPENDIX C: The Well Inventory Database ...................................................................................... 65GLOSSARY OF TERMS...................................................................................................................... 66
LIST OF TABLES Table i. 2017 summary of well sampling results from DPR and SWRCB, and previously unreported
USGS data. ................................................................................................................................ iTable 1. Summary of well sampling results for 2017 and previously unreported USGS data. ................ 8Table 2. DPR response to agricultural use pesticide detections reported in 2017 and previously
unreported detections by the USGS. ........................................................................................ 37
LIST OF FIGURES IN APPENDICES APPENDIX A, Figure A-1. Fresno County GWPAs. ............................................................................. 60APPENDIX A, Figure A-2. Ground Water Protection Areas. ............................................................... 61APPENDIX A, Figure A-3. Locations of Proposed and Existing GWPAs in the Southern San Joaquin
Valley
. ..................................................................................................................................... 62APPENDIX C, Figure C-1. Wells in the DPR Well Inventory Database. ................................................. 65
APPENDIX D: Well Sampling Results Summarized by County and Pesticide............................................. 73
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BACKGROUND
PROTECTING GROUNDWATER FROM PESTICIDE CONTAMINATION — THE PCPAThe Department of Pesticide Regulation (DPR) began addressing pesticide contamination of groundwater in the early 1980s after the discovery of 1,2-dibromo-3-chloropropane (DBCP) in well water. Subsequent reports of pesticides in groundwater led to passage of the Pesticide Contamination Prevention Act (PCPA) of 1985, an act designed to prevent pesticide pollution 3 of groundwater by agricultural use pesticides, with emphasis on the protection of public drinking water supplies.5
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The PCPA of 1985 added Article 15 (sections 13141 – 13152) to the Food and Agricultural Code (FAC). FAC section 13150 allows the continued sale and use of detected pesticides provided certain conditions for use have been met. DPR authorizes use modifications of detected pesticides under the Restricted Materials permit program (Title 3, California Code of Regulations [3CCR] section 6400 et seq.), implemented by California’s County Agricultural Commissioners (CACs).
The PCPA authorized establishment of a program that identifies pesticides that have the potential to pollute groundwater. 6 Under this program, DPR is required to conduct groundwater sampling, maintain a database of wells sampled for pesticides, and conduct a formal review to determine if use of detected pesticides can be modified to protect groundwater.
To implement the PCPA, DPR:
Obtains physical/chemical/environmental fate data from pesticide registrants to support theregistration of agricultural use pesticides; maintains the data in DPR’s Pesticide Chemistry Database(see Pesticide Data Index).
Uses data in the Pesticide Chemistry Database to establish persistence and mobility thresholdvalues called specific numerical values (SNVs)7 and evaluates the groundwater pollutionpotential of agricultural use pesticides based (in part) on these values. NOTE: Senate Bill (SB)1117 modified the process for determining pollution potential by requiring DPR to develop apeer reviewed method 8 (in consultation with a subcommittee of the Director’s PesticideRegistration and Evaluation Committee) to determine the potential of a pesticide to pollutegroundwater using SNVs. This revised procedure is currently under development.
3 The PCPA added sections 13141-13152 to the FAC. 3CCR sections 6416-6487.5 and 6800-6804 implement these FAC sections.
4 FAC section 13142 defines “pollution” as “the consequence of polluting,” and “pollute” as “…to introduce a product into the groundwaters of the state resulting in an active ingredient, other specified ingredient, or a degradation product of a pesticide above a level that does not cause adverse health effects, accounting for an adequate margin of safety.”
5 California’s definition of “agricultural use” is broad and includes not only pesticides used in production agriculture, but also those used on turf (e.g., golf courses, cemeteries) and along rights-of-way.
6 See DPR’s Groundwater Protection Program.
7 SNV threshold values for all parameters are listed in 3CCR section 6804.
8 Peer review is conducted using the process described in section 57004 of the Health and Safety Code.
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Compiles the Groundwater Protection List (GWPL) that includes agricultural use pesticideactive ingredients, other specified ingredients, and degradation products that have thepotential to pollute groundwater. Also added are pesticides whose use has been modifiedfollowing their detection in groundwater.10
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Utilizes contaminant transport modeling tools to:o Evaluate the contamination potential of pesticides prior to their California registration;o Prioritize pesticides for monitoring; ando Define Ground Water Protection Areas (GWPAs).11
Monitors for agricultural use pesticides on the GWPL and their degradates to determine if theyhave migrated to groundwater.
Evaluates reported pesticide and degradate detections in groundwater, including thosereported by other agencies.12
Determines whether detection of a pesticide in groundwater is the result of legal agriculturaluse and if so, conducts a formal review process to determine if the pesticide’s use can bemodified to prevent pollution.
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Conducts ongoing groundwater monitoring of pesticides whose continued use has beenmodified to prevent pollution.
Continuously reviews new science and data that could impact the validity of a finding that apesticide has not polluted and does not threaten to pollute the groundwater of the state.
Resubmits a pesticide to the formal review process if new information indicates that continueduse of a previously reviewed pesticide threatens to pollute the groundwater of the state.
9 The Groundwater Protection List (3CCR section 6800) is divided into two parts. Section 6800(a) includes seven chemicals that have been detected in groundwater or soil and are regulated as groundwater contaminants: atrazine, bentazon, bromacil, diuron, norflurazon, prometon, and simazine. Section 6800(b) includes 98 chemicals that have the potential to become groundwater contaminants based on their mobility, persistence, and legal uses. SB 1117 requires DPR to “…include on the GWPL each active ingredient, other specified ingredient, and degradation product of a pesticide that, when applied, has the potential to pollute groundwater.”
10 Previously detected pesticides on the GWPL (3CCR section 6800[a]) include: atrazine, bentazon (Basagran®), bromacil, norflurazon, prometon, simazine, and diuron (except diuron products with less than 7% diuron that are applied to foliage).
11 See Appendix A for more information on GWPAs.
12 See Appendix B for a list of reporting agencies and a discussion of their role in the PCPA process.
13 Legal agricultural uses include pesticide applications made in accordance with the registered pesticide label.
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In addition, DPR:
Maintains a database of pesticide detections in groundwater reported to DPR by local, county, andstate agencies.14
Prepares an annual Well Sampling Report that summarizes monitoring results and specifies actionstaken by DPR in response to detections from nonpoint agricultural sources. Annual Well SamplingReports are available at: http://www.cdpr.ca.gov/docs/emon/grndwtr/wellinv/wirmain.htm.
IDENTIFYING POTENTIAL GROUNDWATER CONTAMINANTS UNDER THE PCPADPR developed several evaluation procedures to estimate a pesticide’s potential to pollute groundwater. These procedures are described below.
Using Environmental Fate Data to Predict Pesticide Behavior in the EnvironmentThe PCPA required DPR to establish threshold SNVs for six physical/chemical parameters presumed to be correlated to a pesticide’s potential to leach to groundwater: water solubility, soil organic carbon coefficient (Koc), hydrolysis half-life, aerobic soil metabolism half-life, anaerobic soil metabolism half-life, and field dissipation half-life. Water solubility and Koc are indicators of mobility within the soil, while hydrolysis half-life, aerobic and anaerobic soil metabolism, and field dissipation are indicators of persistence of the pesticide in soil. A pesticide is predicted to have the potential to leach to groundwater if it is both mobile and persistent.
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DPR developed threshold SNVs by evaluating nationwide groundwater studies and performing a statistical comparison of the physical/chemical attributes of pesticides detected in groundwater as a result of legal agricultural use (called leachers), and pesticides not detected (nonleachers). Analysis showed data for water solubility, hydrolysis half-life, Koc, and anaerobic soil metabolism half-life were significantly different for leachers and nonleachers (Johnson, 1991). However, leacher and nonleacher aerobic soil metabolism data were not significantly different.17
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After establishing threshold SNVs, DPR scientists used the data to characterize a pesticide’s behavior in the environment. Pesticides that exceed at least one mobility SNV, one persistence SNV, and are applied under specific conditions are placed on the GWPL and monitored to determine if they have migrated to groundwater as a result of their legal agricultural use.
14 See Appendix C for more information on the Well Inventory Database.
15 Although DPR has not established an SNV for field dissipation data, these data are used in modeling procedures to assess the leaching potential of new products proposed for registration.
16 An evaluation of SNVs for these properties resulted in the identification of 90 percent of the chemicals found in groundwater due to legal agricultural use.
17 Because the PCPA requires DPR to establish an SNV for each physical/chemical parameter, and because soil metabolism half-life appears to be an ineffective predictor of a pesticide’s groundwater contamination potential, the SNV for aerobic soil metabolism half-life is set at a value that minimizes its importance in the discrimination procedure.
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SB 1117 modified the process for estimating pollution potential by requiring DPR to develop a peer reviewed SNV-based method in consultation with a subcommittee of the Director’s Pesticide Registration and Evaluation Committee. This revised procedure is currently under development.
Using Computer Modeling Tools to Predict Pesticide Contamination PotentialIn addition to evaluating the contamination potential of agricultural use pesticides by comparing SNV values, DPR scientists use two models to predict pesticide behavior.18
LEACHM, the leaching estimation and chemistry model (Hutson, 2003) is a pesticide fateand transport modeling tool used to evaluate the leaching potential of a pesticide. Themodel enables DPR scientists to predict a pesticide’s movement through the root zone of aleaching-vulnerable soil (Spurlock, 2000) and predict the occurrence and magnitude of wellwater concentrations based upon mobility and persistence data, label information, climatedata, and label-recommended irrigation practices (Troiano and Clayton, 2009). If thepesticide is determined to be a potential groundwater contaminant following theevaluation, the registrant is required to take steps (e.g., amending the product label orcommitting to a stewardship program) to mitigate the potential threat to groundwaterbefore DPR will approve the pesticide for use in California. If mitigation is not possible,California registration is denied.
CALVUL, the California vulnerability model is used to evaluate areas of California that arevulnerable to pesticide contamination based on soil type and depth-to-groundwater. Ifpesticide use on a given section of land is deemed likely to result in groundwatercontamination, the section is designated a GWPA.19
MONITORING FOR PESTICIDES—PRIORITIZING THE CANDIDATES
Pesticides predicted to have the potential to contaminate groundwater are ranked for annual monitoring. This ranking enables DPR to focus limited resources on pesticides that present the greatest contamination risk. DPR assigns highest priority to California registered agricultural use pesticides that are:
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On the GWPL; 21
18 The data used in these models are maintained in DPR’s Pesticide Chemistry Database. The database includes pesticide mobility and persistence data submitted by pesticide registrants.
19 To use a pesticide regulated as a groundwater contaminant in a GWPA, users must obtain a Restricted Materials permit from their County Agricultural Commissioner. These permits specify the enforceable management practices required for use in each type of GWPA. For more information on GWPAs, see Appendix A.
20 For more information on pesticide monitoring ranking see: Clayton, M. 2011, Selection of Pesticide Active Ingredients for Future Analytical Method Development and Ground Water Monitoring. Available at: http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/analysis_memos/ai_priorities_2011_2304-ross.pdf
21 DPR samples groundwater for pesticides on the GWPL to: 1) determine if pesticides identified as potential contaminants have migrated to groundwater as a result of their legal agricultural use; 2) expand GWPAs if additional detections are made; and 3) assess the effectiveness of mitigation measures used in the GWPAs.
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Reported as detections in groundwater by public agencies (see Appendix B for a list ofreporting agencies);
Believed to have a higher likelihood of contaminating groundwater based on computersimulated transport modeling or based upon a review of new science and data that indicatethe pesticide could potentially pollute groundwater;
Used intensively, or whose use is increasing (coupled with other risk factors such aspersistence and mobility in soil); or
Injected into the soil by ground-based application equipment, or applied by chemigation,or followed within 72 hours by flood or furrow irrigation.
DPR also assigns a higher priority to pesticides that:
Have been detected previously in California (or nationwide); and
Have no monitoring history in California.
RESPONDING TO PESTICIDE DETECTIONS IN GROUNDWATER
DPR conducts sampling to confirm detections of agricultural use pesticides, but does not conduct additional sampling if the detected pesticide is:
No longer registered for use as a pesticide in California (e.g., detections from legacypesticide use or from non-pesticidal use);
Reported in error or is an invalid detection due to unacceptable analytical variability;
Not detected in follow-up samples taken by the reporting agency;
Detected at a concentration below DPR’s Screening Level (less than 80 percent of DPR’sanalytical reporting limit; screening level of 0.04 ppb);
Regulated as a groundwater contaminant under 3CCR section 6800(a) and detected in aGWPA (where use of the pesticide is regulated);
Registered for use as a pesticide but also occurs naturally (such as copper); or
Detected in a private well that DPR does not have permission to sample. DPR will defersampling and place a pesticide on a “watch list” if the pesticide was detected at less than80 percent of DPR’s analytical reporting limit, or if DPR is unable to develop an analyticalmethod that meets the criteria necessary to validate the detection.
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If groundwater detections of an active ingredient or its degradates are determined to be from a pesticide’s legal agricultural use, the findings are subject to a formal review process to determine if the pesticide’s use can continue under modified conditions. If it is determined use can be modified to the extent that there is a high probability it will not pollute, DPR adds the pesticide to the GWPL and requires applicators to adopt mitigation measures when applying the pesticide in GWPAs. Detections of agricultural use pesticides (or their degradates or other specified ingredients) that do not trigger the formal review process are placed on a “watch list” and tracked by DPR for changes in detection concentration or frequency.
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If a detected pesticide is added to the GWPL and regulated as a groundwater contaminant under 3CCR section 6800(a)—and the well is located in a GWPA—regulation of use under the Restricted Materials permit program is believed to constitute an adequate response to detections unless concentrations are high enough to indicate existing mitigation measures are not adequate to prevent pollution. If the well is not located in a GWPA, DPR may establish a GWPA that includes the well site if: 1) the well is in a section of land that is adjacent to an existing GWPA, or 2) the pesticide is detected in two or more wells within a four-section area that is not adjacent to an existing GWPA. (For more information on GWPAs, see Appendix A.)
Areas of Non-AuthorizationState law does not authorize DPR to regulate pesticide use when detections in groundwater are the result of manufacturing processes, accidental spills/releases, or illegal disposal; DPR refers these detections to the SWRCB for further investigation.
ASSESSING THE EFFECTIVENESS OF MITIGATION MEASURES
In 1999, DPR established a well monitoring network to evaluate baseline pesticide concentrations in an effort to measure the effectiveness of groundwater protection regulations. Currently, DPR’s well monitoring network includes 61 shallow, domestic wells located in runoff and/or leaching GWPAs in Fresno and Tulare counties. Preliminary analysis suggests that regulatory action taken by DPR has resulted in measurable decreases in both detection frequencies and well water concentrations for many regulated pesticides (Garretson, 1999 and 2012).
22 Pesticides that have been subject to the formal review process include aldicarb (1988); atrazine (1986); bentazon (1989); bromacil (1986); chlorthal dimethyl (2018); diuron (1986); hexazinone (2010); metolachlor/S-metolachlor (2016); norflurazon (1998); prometon (1986); and simazine (1986). With the exception of aldicarb, chlorthal dimethyl, hexazinone, and metolachlor/S-metolachlor, it was determined the agricultural use of these pesticides could be modified so there would be a high probability that their continued use would not pollute groundwater. In 1988, statewide use restrictions were adopted for aldicarb. Chlorthal dimethyl (2018), hexazinone (2010), and metolachlor/S-metolachlor (2016) were determined not to have polluted or threatened to pollute groundwater in the state, but continued monitoring of each was recommended.
Another pesticide recently placed in the formal review process was alachlor (2016). The formal review of alachlor was suspended due to the imminent federal cancellation of all alachlor products.
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SAMPLING RESULTS
DETECTIONS OF PESTICIDES AND RELATED DEGRADATES
This annual report includes well sampling data from DPR and SWRCB for the sampling period of January through December 2017. This report also includes previously unreported well sampling data from the USGS for the sampling period of May 2011 through December 2016. Table 1 includes the well sampling data from all three agencies.
Over 5,600 (5,635) wells were sampled for one or more of 315 agricultural use pesticides and pesticide degradates. Of the wells sampled, 786 wells tested positive for one or more pesticides/ degradates. Sampling efforts yielded detections of 86 pesticides/degradates, 18 of which are not registered for use in California.
Sampling data was collected from wells in 57 counties; San Francisco County was not sampled by any agency in calendar year 2017 or the previously unreported USGS data. Forty-two counties had wells with detections. (See Appendix D for county sampling results.)
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Table 1. Summary of well sampling results for 2017 and previously unreported USGS data.
Pesticide or Degradate
SamplesTaken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
1,2-D + 1,3-D + C-3 pesticides 4,336 0
2,290 0
48 0 0.05 -- SWRCB
1,2-Dicloropropane (1,2-D) (propylene dichloride)2
6,694 145
4,046 94
57 15 0 - 0.5 0.001 - 2.6 SWRCB
USGS
1,3-D (1,3-dichloropropene) (Telone®)
6,415 0
3,384 0
56 0 0 - 0.5 -- SWRCB
USGS
1,4-Dichlorobenzene (p-DCB)1 1,138 8
1,042 7
51 5 0 - 0.1 0.011 - 3.26 USGS
1-Naphthol(degradate of carbaryl)
602 0
563 0
47 0 0.036 - 0.072 -- USGS
2-(1-Hydroxyethyl)-6-methylaniline (degradate of acetochlor)
277 0
270 0
24 0 0 - 1 -- USGS
2,4,5-T (2,4,5-tichloro phenoxy acetic acid)
461 0
369 0
24 0 0.09 - 2 -- SWRCB
2,4,5-Trichlorophenol 48 0
48 0
3 0 5.1 - 53 -- USGS
2,4,6-Trichlorophenol 68 0
58 0
4 0 4 - 43 -- SWRCB
USGS
2,4-D (2,4-dichlorophenoxy-acetic acid)1
1,559 1
1,240 1
47 1 0 - 10 0.03 SWRCB
USGS
Pesticide or Degradate
SamplesTaken
Positive Samples
WellsSampled
Wells withDetections
CountiesSampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
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2,4 Xylenol- 480
480
30 5.1 - 53 -- USGS
2,6-Diethylaniline (degradate of alachlor)2
6022
5632
472 0.006 0.001 - 0.003 USGS
2-Aminobenzimidazole(degradate of bentazon)
2880
2810
240 0 - 0.05 -- USGS
2-Ethyl-6-methylaniline(degradate of metolachlor, diuron, monuron)
6020
5630
470 0.01 - 0.02 -- USGS
2-Hydroxy alachlor(degradate of alachlor)
2880
2810
240 0 - 0.05 -- USGS
2-Hydroxyatrazine(degradate of atrazine)1
2881
2811
241 0 - 0.02 0.003 USGS
2-Isopropyl-6-methyl-4-pyrimidinol(degradate of diazinon)1
2882
2812
242 0 - 0.05 0.033 - 0.079 USGS
3,4-Dichloroaniline (degradate of diuron, propanil)1
60312
56412
4710 0.004 - 0.008 0.006 - 0.089 USGS
3,5-Dichloroaniline (degradate of iprodione, dichloran)1
3505
3135
473 0.004 - 0.006 0.002 - 0.005 USGS
3-PBA(degradate of cypermethrin)
2880
2810
240 0 - 0.25 -- USGS
4(2,4-DB), dimethylamine salt 2450
1840
130 3 - 30 -- SWRCB
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
10
4-CLOC 6020
5630
470 0.005 - 0.008 -- USGS
4-Hydroxy chlorothalonil(degradate of chlorothalonil)1
288 1
281 1
241 0 - 0.1 0.088 USGS
4-Hydroxy molinate(degradate of molinate)
288 0
281 0
240 0 - 0.05 -- USGS
Acephate 288 0
281 0
240 0 - 0.05 -- USGS
ACET (deisopropyl-atrazine or deethyl-simazine) (degradate of atrazine/simazine)1 372
93365 89
2710 0 - 0.05 0.003 - 0.743 DPR
USGS
Acetochlor 1,2160
830 0
520 0 - 0.1 -- SWRCB
USGS
Acetochlor ESA (degradate of acetochlor)
288 0
281 0
240 0 - 0.4 -- USGS
Acetochlor OA (degradate of acetochlor)
573 0
281 0
240 0 - 0.25 -- USGS
Acetochlor sulfinylacetic acid (degradate of acetochlor)
288 0
281 0
240 0 - 0.5 -- USGS
Acifluorfen 114 0
92 0
7 0 0 - 0.5 SWRCB
Acrylonitrile2489
1483
1431 0 - 0.8 0.21 USGS
--
Pesticide or Degradate
Samples Wells Counties ‡ Detected Taken Sampled Sampled Reporting Concentration Sampling
Limit Range Agency(s) Positive Wells with Counties with (ppb) (ppb) Samples Detections Detections
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Alachlor 3,179 0
2,440 0
55 0 0 - 1 --
DPR SWRCB USGS
Alachlor 2nd Amide (degradate of alachlor)
892 0
8050
51 0 0 - 0.02 -- USGS
Alachlor OXA (degradate of alachlor)
576 0
2810
24 0 0 - 0.5 -- USGS
Alachlor sulfinylacetic acid (degradate of alachlor)
288 0
2810
24 0 0 - 0.2 -- USGS
Aldicarb 990 0
8480
45 0 0 - 3 -- SWRCB
USGS
Aldicarb sulfone (degradate of aldicarb)
1,001 0
8590
45 0 0 - 4 -- SWRCB
USGS
Aldicarb sulfoxide (degradate of aldicarb)
1,001 0
8590
45 0 0 - 3 -- SWRCB
USGS
Aldrin 697 0
4410
35 0 0.005 - 0.075 -- SWRCB
Allyl alcohol 633 0
6250
45 0 0 - 5 -- USGS
Alpha-terpineol 633 0
6250
45 0 6 -- USGS
Ametryne 287 0
2810
24 0 0 - 0.01 -- USGS
Pesticide or Degradate
Samples Wells Counties Detected Taken Sampled Sampled ‡Reporting Concentration Sampling
Limit Range Agency(s) Positive Wells with Counties with (ppb) (ppb) Samples Detections Detections
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Anthranilic acid isopropylamide(degradate of bentazon)
2880
2810
24 0 0 - 0.01 -- USGS
Asulam 2860
2810
24 0 0 - 0.25 -- USGS
Atraton 16 0
160
5 0 0.5 -- SWRCB
Atrazine13,422119
2,680104
5525 0 - 0.5 0.001 - 0.6
DPR SWRCB USGS
Azinphos-methyl (Guthion®) 9760
8890
510 0 - 0.12 -- DPR
USGS
Azinphos-methyl-oa (degradate of azinphos-methyl)
8910
8040
51 0 0 - 0.05 -- USGS
Azoxystrobin1 3721
3651
27 1 0 - 0.05 0.002 DPR
USGS
Benefin (benfluralin)1 6023
5633
472 0.014 - 0.038 0.002 - 0.003 USGS
Bensulide (Betasan®) 840
84 0
5 0 0.05 -- DPR
Bentazon (Basagran®)1 1,3294
1,1204
453 0 - 2 0.002 - 0.015
DPR SWRCB USGS
BHC (other than gamma isomer) 2890
118 0
100 0.005 - 0.05 -- SWRCB
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells withDetections
CountiesSampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
13
Bifenthrin 2880
2810
240 0 - 0.1 -- USGS
Bromacil1 1,47848
1,12331
446 0 - 10 0.001 - 5.48
DPR SWRCBUSGS
Bromoxynil phenol 2880
2810
240 0 - 0.079 -- USGS
Butachlor 9190
7010
320 0.3 - 0.38 -- SWRCB
Butralin 2880
2810
240 0 - 0.025 -- USGS
Butylate 2880
2810
240 0 - 0.05 -- USGS
Camphor1 14 2
13 2
21 0.044 - 0.08 0.021 - 0.035 USGS
Captan1189
194 1
71 0.1 0.27 SWRCB
Carbaryl
1,7000
1,4680
540 0 - 5 --
DPRSWRCBUSGS
Carbendazim 2870
2800
240 0 - 0.05 --
USGS
Carbofuran 1,6350
1,3660
540 0 - 5 --
DPR SWRCBUSGS
Pesticide or Degradate
SamplesTaken
Positive Samples
WellsSampled
Wells withDetections
CountiesSampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
SamplingAgency(s)
14
Carbon disulfide2 2,12454
1,50253
5318 0 - 0.5 0.1 - 5.2 SWRCB
USGS
Carbophenothion 1890
94 0
7 0 0 -- SWRCB
Carboxy molinate (degradate of molinate)
2880
2810
240 0 - 0.25 -- USGS
Chlordane 7550
5800
320 0.1 -- SWRCB
Chlorobenzilate 11 0
11 0
1 0 0 -- SWRCB
Chloroneb 110
11 0
1 0 0 -- SWRCB
Chloropicrin1634
1625
1451 0 - 1.88 0.032 USGS
Chlorosulfonamide acid (degradate of halosulfuron)
2880
2810
240 0 - 0.075 -- USGS
Chlorothalonil 1410
1200
130 0.1 - 5 -- SWRCB
Chlorpropham 1840
89 0
7 0 0 -- SWRCB
Chlorpyrifos1 9042
8162
512 0 - 0.16 0.001 - 0.003 SWRCB
USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
CountiesSampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
15
Chlorpyrifos oxon (degradate of chlorpyrifos)
8920
8050
510 0 - 0.08 -- USGS
Chlorsulfuron1288
1281
1241 0 - 0.1 0.007 USGS
Chlorthal dimethyl (dacthal/DCPA)1
6151
5751
471 0 - 0.008 0.001 SWRCB
USGS
Chorimuron ethyl 2880
2810
240 0 - 0.05 -- USGS
Clomazone 760
76 0
5 0 0.05 -- DPR
Cyanazine 8290
6490
510 0 - 0.25 -- SWRCB
USGS
Cyfluthrin 6040
5640
470 0.016 -- USGS
Cyhalothric acid (degradate of bifenthrin)
2860
2790
230 0 - 5 -- USGS
Cypermethrin 6040
5640
470 0.02 -- USGS
DACT (diaminochlorotriazine) (degradate of simazine)1
372110
365106
2712 0 - 0.25 0.001 - 5.05 DPR
USGS
Dacthal acid degradates1 31524
26422
258 0 - 0.1 0.1 - 1.1 SWRCB
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells withDetections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
SamplingAgency(s)
16
Dalapon2 1,008 1
8001
351 5 - 10 83 SWRCB"
DBCP (1,2-dibromo-3-chloropropane)2
5,557 1,501
3,316 370
55 12 0 - 0.4 0.008 - 1.32 SWRCB
USGS
DDD (dichloro diphenyl dichloro ethane) (degradate of DDT)
150 0
118 0
10 0 0.005 - 0.02 -- SWRCB
DDE (dichloro diphenyl dichloro ethylene) (degradate of DDT)
150 0
118 0
10 0 0.005 - 0.01 -- SWRCB
DDT (dichloro diphenyl trichloro ethane) 150 0
118 0
10 0 0.005 - 0.02 -- SWRCB
DDVP (dichlorvos) 898 0
811 0
51 0 0 - 1 -- SWRCB
USBS
DEA (deethyl-atrazine) (degradate of atrazine)1
976 115
889 101
51 22 0 - 0.25 0.002 - 0.276 DPR
USGS
Dechlorofipronil (degradate of fipronil)
288 0
281 0
24 0 0 - 0.01 -- USGS
Dechlorometolachlor (degradate of metolachlor)1
288 3
281 3
24 2 0 - 0.003 0.001 - 0.003 USGS
DEET 14 0
13 0
2 0 0.04 - 0.06 -- USGS
Deiodo flubendiamide (degradate of flubendiamide)
288 0
281 0
24 0 0 - 0.25 -- USGS
Pesticide or Degradate
SamplesTaken
PositiveSamples
Wells Sampled
Wells with Detections
Counties Sampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
17
Deisopropylhydroxyatrazine (degradate of atrazine)
288 0
2810
240 0 - 0.25 -- USGS
Deisopropyl prometryn (degradate of prometryn)
288 0
281 0
24 0 0 - 0.003 -- USGS
Demethyl fluometuron (degradate of fluometuron)2
288 2
281 2
24 1 0 - 0.01 0.001 USGS
Demeton 288 0
281 0
24 0 0 - 0.005 -- USGS
Desisopropyl desethyl atrazine (degradate of atrazine)1
288 3
281 3
24 3 0 - 0.01 0.001 - 0.011 USGS
Desulfinyl fipronil (degradate of fipronil)
288 0
281 0
24 0 0 - 0.004 -- USGS
Desulfinyl fipronil amide (degradate of fipronil)
892 0
805 0
51 0 0 - 0.029 -- USGS
Diazinon 1,862 0
1,540 0
54 0 0 - 2 --
DPR SWRCBUSGS
Diazoxon 3550
3480
280 0 - 0.012 -- USGS
Dicamba 981 0
806 0
43 0 0 - 1.5 -- SWRCB
USGS
Dichloran 76 0
76 0
5 0 0.05 -- DPR
Pesticide or Degradate
Wells Sampled
Wells with Detections
Samples Taken
Positive Samples
Counties Sampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
Dichlobenil (Casaron®) 760
76 0
18
50 0.05 -- DPR
Dichlorprop, butoxyethanol ester 1890
1280
120 0 - 5 -- SWRCB
Dicrotophos 8890
8030
510 0 - 0.16 -- USGS
Dieldrin21,119
2947
2512 0.005 - 0.071 0.011 - 0.065 SWRCB
USGS
Diflubenzuron1287
1280
1241 0 - 0.01 0.002 USGS
Diflufenzopyr 2880
2810
240 0 - 0.1 -- USGS
Dimethenamid 372 0
3650
270 0 - 0.05 -- DPR
USGS
Dimethenamid ESA (degradate of dimethenamid)1
576 1
2811
241 0 - 0.189 0.01 USGS
Dimethenamid OA (degradate of dimethenamid)
288 0
2810
240 0 - 0.25 -- USGS
Dimethoate 1,9550
1,626 0
540 0 - 20 --
DPR SWRCB USGS
Dinoseb 1,1110
8230
360 0.2 - 2 -- SWRCB
Pesticide or Degradate
SamplesTaken
Positive Samples
Wells Sampled
Wells withDetections
Counties Sampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
SamplingAgency(s)
19
Diphenamid 1920
950
70 100 -- SWRCB
Diquat dibromide 1,0580
765 0
37 0 2 - 4 -- SWRCB
Disulfoton 874 0
712 0
51 0 0 - 0.05 --
DPRSWRCBUSGS
Disulfoton oxon sulfone (degradate of disulfoton)
2880
2810
240 0 - 0.025 -- USGS
Disulfoton oxon sulfoxide (degradate of disulfoton)
288 0
281 0
24 0 0 - 0.01 -- USGS
Disulfoton sulfone (degradate of disulfoton)
640 0
558 0
51 0 0 - 0.05 -- USGS
Diuron1474 44
383 35
29 6 0 - 1 0.002 - 0.189
DPR SWRCB USGS
Diuron-desdimethyl (degradate of diuron)
2880
2810
240 0 - 0.25 -- USGS
Diuron-desmethyl (degradate of diuron)1
288 23
281 23
24 6 0 - 0.05 0.001 - 0.023 USGS
DNOC, sodium salt 48 0
48 0
3 0 10 - 110 -- USGS
DSMN (desmethyl norflurazon or demethylnorflurazon) (degradate of norflurazon)1
372 54
365 53
27 6 0 - 0.05 0.001 – 1.17 DPR
USGS
Pesticide or Degradate
SamplesTaken
PositiveSamples
Wells Sampled
Wells withDetections
Counties Sampled
Counties withDetections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
20
Endosulfan 1500
1180
100 0.005 - 0.01 -- SWRCB
Endosulfan I 3520
3140
47 0 0.006 - 0.01 -- USGS
Endosulfan II 1500
1180
10 0 0.005 - 0.01 -- SWRCB
Endosulfan sulfate (degradate of endosulfan)
5310
4290
48 0 0.005 - 0.05 -- SWRCB
USGS
Endothall 1,148 0
6740
37 0 2 - 45 -- SWRCB
Endrin 7980
5810
32 0 0.005 - 0.1 -- SWRCB
Endrin aldehyde 1500
1180
10 0 0.01 - 0.05 -- SWRCB
EPTC (S-ethyl-dipropylthiocarbamate)1 8613
6693
52 3 0 - 1 0.007 - 0.015 SWRCB
USGS
Ethion 6100
5700
47 0 0 - 0.01 -- SWRCB
USGS
Ethion monooxon (degradate of ethion)
5650
5280
46 0 0.021 -- USGS
Ethofumesate 84 0
84 0
50 0.05 -- DPR
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
21
Ethoprop (prophos) 7140
633 0
510 0 - 0.05 -- DPR
USGS
Ethylene dibromide (EDB)2 4,924 30
3,2059
554 0 - 0.028 0.008 - 0.17 SWRCB
USGS
Ethylene dichloride21,124
31,036
3512 0 - 0.2 0.09 - 0.26 USGS
Ethyl-methylphenyl-aminopropanol(degradate of metolachlor)
288 0
281 0
240 0 - 0.05 -- USGS
Etoxazole 288 0
281 0
240 0 - 0.05 -- USGS
Famoxadone 150 0
147 0
210 0.06 - 0.25 -- USGS
Fenamiphos 943 0
874 0
510 0 - 0.05 -- DPR
USGS
Fenamiphos sulfone (degradate of fenamiphos)
891 0
804 0
510 0 - 0.054 -- USGS
Fenamiphos sulfoxide (degradate of fenamiphos)
882 0
795 0
510 0 - 0.08 -- USGS
Fenbutatin-oxide (Vendex®) 288 0
281 0
240 0 - 0.1 -- USGS
Fentin hydroxide 288 0
281 0
240 0 - 0.25 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
22
Fipronil 8920
805 0
510 0 - 0.018 -- USGS
Fipronil sulfide (degradate of fipronil)1
8925
805 5
515 0 - 0.016 0.003 - 0.007 USGS
Fipronil sulfonate (degradate of fipronil)1
2881
281 1
241 0 - 0.1 0.107 USGS
Fipronil sulfone (degradate of fipronil)1
8921
805 1
511 0 - 0.024 0.003 USGS
Fipronil-carboxamide (degradate of fipronil)1
2881
281 1
241 0 - 0.01 0.003 USGS
Flubendiamide 2880
281 0
240 0 - 0.01 -- USGS
Fludioxonil1 84 1
84 1
5 1 0.05 0.066 DPR
Flumetsulam 2810
274 0
240 0 - 0.05 -- USGS
Fluometuron2288
2281
2242 0 - 0.05 0.01 USGS
Fonofos (Dyfonate®) 9680
881 0
510 0 - 0.05 -- DPR
USGS
Glyphosate1784
1582
1371 20 - 25 50 SWRCB
Pesticide or Degradate
Samples Tak
PosiSam
en
tive ples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
23
Halosulfuron-methyl 288 0
281 0
24 0 0 - 0.05 -- USGS
Heptachlor 754 0
577 0
32 0 0.005 - 0.01 -- SWRCB
Heptachlor epoxide 756 0
578 0
32 0 0.005 - 0.01 -- SWRCB
Hexachlorobenzene 918 0
686 0
39 0 0.01 - 11 -- SWRCB
USGS
Hexazinone1976 22
889 20
51 15 0 - 0.05 0.001 - 0.353 DPR
USGS
Hydroxy didemethyl fluometuron (degradate of fluometuron)
288 0
281 0
24 0 0 - 0.25 -- USGS
Hydroxy monodemethyl fluometuron (degradate of fluometuron)2
288 1
281 1
24 1 0 - 0.05 0.009 USGS
Hydroxyacetochlor (degradate of acetochlor)
288 0
281 0
24 0 0 - 0.05 -- USGS
Hydroxycarbofuran (degradate of carbofuran)
1,000 0
858 0
45 0 0 - 3 -- SWRCB
USGS
Hydroxydiazinon (degradate of diazinon)
288 0
281 0
24 0 0 - 0.05 -- USGS
Hydroxyfluometuron (degradate of fluometuron)
288 0
281 0
24 0 0 - 0.05 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
24
Hydroxymetolachlor (degradate of metolachlor)1
288 4
281 4
24 3 0 - 0.01 0.001 - 0.005 USGS
Hydroxysimazine (degradate of simazine)1
288 1
281 1
24 1 0 - 0.25 0.003 USGS
Hydroxytebuthiuron (degradate of tebuthiuron)
288 0
281 0
24 0 0 - 0.05 -- USGS
Imazamox 288 0
281 0
24 0 0 - 0.05 -- USGS
Imazaquin2288
1281
124 1 0 - 0.05 0.004 USGS
Imazethapyr1 288 1
281 1
24 1 0 - 0.05 0.005 USGS
Imidacloprid1372
9365
927 1 0 - 0.05 0.006 - 5.97 DPR
USGS
Indoxacarb 288 0
281 0
24 0 0 - 0.05 -- USGS
Iprodione 604 0
564 0
47 0 0.014 -- USGS
Isofenphos 604 0
564 0
47 0 0.006 - 0.014 -- USGS
Isoxaflutole 274 0
267 0
23 0 0 - 0.05 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
25
Kresoxim-methyl 288 0
281 0
24 0 0 - 0.05 -- USGS
Lactofen 285 0
278 0
24 0 0 - 0.25 -- USGS
Lambda-cyhalothrin 352 0
314 0
47 0 0.01 - 0.014 -- USGS
Lindane (gamma-BHC) 898 0
656 0
37 0 0.005 - 0.2 -- SWRCB
Linuron1372
2 365
227 2 0 - 0.05 0.001 - 0.002 DPR
USGS
Malaoxon 885 0
799 0
51 0 0 - 0.022 -- USGS
Malathion1967
1881
151 1 0 - 0.05 0.004 DPR
USGS
MCPA 246 0
241 0
24 0 0 - 0.25 -- USGS
MCPA, dimethylamine salt 56 0
17 0
4 0 10 - 100 -- SWRCB
MCPP (2-(4-chloro-2-methylphenoxy) propionic acid)
56 0
17 0
4 0 10 - 100 -- SWRCB
Merphos 1 0
1 0
1 0 2 -- SWRCB
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit
Detected Concentration
Range (ppb) (ppb)
Sampling Agency(s)
26
Metalaxyl 990 0
899 0
51 0 0 - 0.16 -- DPR
USGS
Metam sodium 1 0
1 0
1 0 0.006 -- USGS
Metconazole 288 0
281 0
24 0 0 - 0.01 -- USGS
Methamidophos 288 0
281 0
24 0 0 - 0.05 -- USGS
Methidathion 892 0
805 0
51 0 0 - 0.02 -- USGS
Methiocarb 464 0
416 0
32 0 0.05 - 5 -- DPR
SWRCB
Methomyl 1,000 0
858 0
45 0 0 - 2 -- SWRCB
USGS
Methomyl oxime (degradate of methomyl)
199 0
194 0
21 0 0 - 2 -- USGS
Methoxychlor 874 0
638 0
36 0 0.005 - 10 -- SWRCB
Methoxyfenozide1288 16
281 16
24 7 0 - 0.005 0.001 - 0.286 USGS
Methyl bromide 4,862 0
3,046 0
56 0 0 - 2 -- SWRCB
USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
27
Methyl iodide2 489 1
483 1
43 1 0 - 0.26 0.04 USGS
Methyl paraoxon (degradate of parathion)
892 0
805 0
51 0 0 - 0.05 -- USGS
Methyl parathion 680 0
640 0
47 0 0.008 - 0.05 -- DPR
USGS
Metolachlor1 1,978 10
1,63710
54 7 0 - 20 0.001 - 0.105
DPR SWRCBUSGS
Metolachlor ESA (degradate of metolachlor)1
28813
28113
246 0 - 0.1 0.004 - 4.37 USGS
Metolachlor hydroxy morpholinone (degradate of metolachlor)
288 0
281 0
24 0 0 - 0.25 -- USGS
Metolachlor OXA (degradate of metolachlor)1
288 2
281 2
24 2 0 - 0.25 0.11 - 0.213 USGS
Metribuzin12,000
11,626
1 54 1 0 - 2 0.007
DPR SWRCBUSGS
Metribuzin DA 5730
281 0
240 0 - 0.25 -- USGS
Metribuzin-DK (degradate of metribuzin)
251 0
244 0
24 0 0 - 0.5 -- USGS
Mevinphos 1 0
1 0
1 0 0.5 -- SWRCB
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
28
Mirex 2 0
2 0
1 0 0 -- SWRCB
Molinate22,086
11,682
1 551 0 - 2 0.004 SWRCB
USGS
MTP (degradate of dacthal)
288 0
281 0
240 0 - 2 -- USGS
Myclobutanil1 892 1
805 1
511 0 - 0.05 0.01 USGS
Naled 271 0
264 0
230 0 - 0.25 -- USGS
Napropamide 84 0
84 0
5 0 0.05 -- DPR
Nicosulfuron1287
1280
1241 0 - 0.014 0.001 USGS
Norflurazon1456 38
365 26
273 0 - 0.05 0.001 - 0.374 DPR
USGS
Novaluron 283 0
276 0
240 0 - 0.25 -- USGS
o-Cresol 48 0
48 0
3 0 5.1 - 53 -- USGS
O-Ethyl O-methyl S-propyl phosphorothioate(degradate of ethoprop)
288 0
281 0
240 0 - 0.01 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range Sampling Agency(s)
(ppb)
29
O-Ethyl S-methyl S-propyl phosphorodithioate(degradate of ethoprop)
288 0
281 0
24 0 0 - 0.05 -- USGS
O-Ethyl S-propyl phosphorothioate(degradate of ethoprop)
288 0
281 0
24 0 0 - 0.25 -- USGS
Omethoate (degradate of dimethoate)
288 0
281 0
24 0 0 - 0.005 -- USGS
Ortho-dichlorobenzene 5,5790
3,0670
52 0 0.5 -- SWRCB
Orthosulfamuron 288 0
281 0
24 0 0 - 0.05 -- USGS
Oryzalin1372
3 365
3 27 3 0 - 0.05 0.004 - 0.036 DPR
USGS
Oxamyl1 1,2811
1,0031
45 1 0 - 20 0.001 SWRCB
USGS
Oxamyl oxime (degradate of oxamyl)
288 0
281 0
24 0 0 - 0.05 -- USGS
Oxydisulfoton (degradate of disulfoton)2
288 1
281 1
24 1 0 - 0.005 0.003 USGS
Oxyfluorfen 628 0
549 0
50 0 0 - 1 -- USGS
Para-chloro-meta-cresol 48 0
48 0
3 0 5.1 - 53 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
30
Paraquat dichloride 24 0
20 0
2 0 20 -- SWRCB
Parathion or ethyl parathion 76 0
76 0
5 0 0.05 -- DPR
Paroxon 288 0
281 0
24 0 0 - 0.025 -- USGS
PCNB (pentachloronitrobenzene) 6 0
6 0
2 0 0.1 -- SWRCB
p-Cresol2 62 3
61 3
5 2 0.08 - 110 0.01 - 0.08 USGS
Pendimethalin1892
1805
151 1 0 - 0.05 0.011 USGS
Pendimethalin metabolite (degradate of pendimethalin)
283 0
278 0
24 0 0 - 0.25 -- USGS
Pentachlorophenol (PCP) 55 0
54 0
4 0 1.6 - 53 -- USGS
Permethrin 903 0
816 0
51 0 0 - 0.05 -- SWRCB
USGS
Permethrin, other related compounds 299 0
292 0
25 0 0 - 0.05 -- SWRCB
USGS
Phorate 968 0
881 0
51 0 0 - 0.05 -- DPR
USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
31
Phorate sulfone (degradate of phorate)
288 0
281 0
24 0 0 - 0.05 -- USGS
Phorate sulfoxide (degradate of phorate)
288 0
281 0
24 0 0 - 0.01 -- USGS
Phoratoxon 854 0
787 0
51 0 0 - 0.25 -- USGS
Phoratoxon sulfone (degradate of phoratoxon)
283 0
276 0
24 0 0 - 0.05 -- USGS
Phoratoxon sulfoxide (degradate of phoratoxon)
281 0
274 0
24 0 0 - 0.05 -- USGS
Phosmet (Imidan®) 584 0
546 0
47 0 0.08 - 0.14 -- USGS
Phosmet-oa (degradate of phosmet)
564 0
529 0
47 0 0.051 -- USGS
Phostebupirim 288 0
281 0
24 0 0 - 0.005 -- USGS
Picloram 986 0
787 0
35 0 0.05 - 1 -- SWRCB
Piperonyl butoxide 357 0
350 0
27 0 0 - 0.25 -- DPR
USGS
P-Nitrophenol(degradate of ethyl parathion)
48 0
48 0
3 0 25 - 270 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
32
Profenofos 281 0
274 0
24 0 0 - 0.01 -- USGS
Prometon11,277
271,004
245111 0 - 0.5 0.002 - 0.151
DPR SWRCBUSGS
Prometryn 1,2350
1,0400
52 0 0 - 2 --
DPRSWRCB USGS
Propachlor 1,3910
7260
34 0 0 - 0.5 -- SWRCB
Propanil1 716 2
634 2
51 2 0 - 0.05 0.005 - 0.06 DPR
USGS
Propargite 640 0
558 0
51 0 0 - 0.05 -- USGS
Propazine2288
4281
424 3 0 - 0.05 0.001 - 0.006 USGS
Propiconazole1640
1558
151 1 0 - 0.01 0.005 USGS
Propoxur1 669 10
614 10
42 4 0 - 5 0.001 - 0.003 SWRCB
USGS
Propyzamide 892 0
805 0
51 0 0 - 0.05 -- USGS
Prosulfuron 288 0
281 0
24 0 0 - 0.05 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
33
Pymetrozine 93 0
92 0
11 0 0.002 - 0.25 -- USGS
Pyraclostrobin 288 0
281 0
24 0 0 - 0.003 -- USGS
Pyridaben 288 0
281 0
24 0 0 - 0.05 -- USGS
Pyriproxyfen 288 0
281 0
24 0 0 - 0.003 -- USGS
Secbumeton 16 0
16 0
5 0 0.5 -- SWRCB
Siduron 288 0
281 0
24 0 0 - 0.05 -- USGS
Silvex 1,021 0
795 0
35 0 0.07 - 1 -- SWRCB
Simazine14,290 219
2,701 176
55 25 0 - 1 0.001 - 0.128
DPR SWRCBUSGS
Sulfentrazone1288
1281
1241 0 - 0.05 0.002 USGS
Sulfometuron methyl1 288 2
281 2
24 2 0 - 0.004 0.001 - 0.002 USGS
Sulfosulfuron1288
1281
124 1 0 - 0.05 0.001 USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
34
Sulfosulfuron ethyl sulfone (degradate of sulfosulfuron)
288 0
281 0
24 0 0 - 0.01 -- USGS
Tebuconazole 288 0
281 0
24 0 0 - 0.05 -- USGS
Tebufenozide1288
1281
124 1 0 - 0.003 0.001 USGS
Tebupirimfos oxon (degradate of tebupirimfos)
288 0
281 0
24 0 0 - 0.01 -- USGS
Tebuthiuron1997 20
888 18
51 10 0 - 0.056 0.002 - 0.121 DPR
USGS
Tebuthiuron degradate 104 288 0
281 0
24 0 0 - 0.05 -- USGS
Tebuthiuron TP 109 (OH) (degradate of tebuthiuron)
288 0
281 0
24 0 0 - 0.25 -- USGS
Tefluthrin 352 0
314 0
47 0 0.01 - 0.014 -- USGS
Terbacil 575 0
441 0
35 0 0 - 0.25 -- SWRCB
USGS
Terbufos 858 0
790 0
51 0 0 - 0.018 -- USGS
Terbufos oxon (degradate of Terbufos)
288 0
281 0
24 0 0 - 0.01 -- USGS
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit
Detected Concentration
Range Sampling Agency(s)
(ppb) (ppb)
35
Terbufos oxon sulfone (degradate of Terbufos)
1,1800
805 0
51 0 0 - 0.05 -- USGS
Terbufos oxon sulfoxide (degradate of Terbufos)
288 0
281 0
24 0 0 - 0.01 -- USGS
Terbufos sulfoxide (degradate of Terbufos)
288 0
281 0
24 0 0 - 0.005 -- USGS
Terbuthylazine 892 0
805 0
51 0 0 - 0.05 -- USGS
Terbutryn 16 0
16 0
5 0 0.5 -- SWRCB
Tetrachloroethane 5,574 0
3,0640
51 0 0.5 -- SWRCB
Tetraconazole1576
3281
324 3 0 - 0.315 0.001 - 0.037 USGS
Thiabendazole 25 0
25 0
9 0 0.004 -- USGS
Thiamethoxam 84 0
84 0
5 0 0.05 -- DPR
Thiobencarb1
Toxaphene
2,977 1
7660
1,9661
5810
55 1
320
0 - 1
0.5 - 1
0.003
--
DPR SWRCBUSGS
SWRCB
36
Pesticide or Degradate
Samples Taken
Positive Samples
Wells Sampled
Wells with Detections
Counties Sampled
Counties with Detections
‡ReportingLimit (ppb)
Detected Concentration
Range (ppb)
Sampling Agency(s)
Trans-propiconazole 3520
314 0
470 0.01 - 0.018 -- USGS
Triallate 2880
281 0
240 0 - 0.05 -- USGS
Tribufos 8910
805 0
510 0 - 0.1 -- USGS
Triclopyr 2880
281 0
240 0 - 0.1 -- USGS
Trifloxystrobin1288
1 281
1241 0 - 0.003 0.001 USGS
Trifluralin1742
4679
4482 0 - 0.022 0.001 - 0.006 SWRCB
USGS
Uniconazole 84 0
84 0
5 0 0.05 -- DPR
Vernolate 16 0
8 0
2 0 1 - 2 -- SWRCB
‡ Some detection values listed in this table are below the reporting limit. Each reporting agency determines the value they will report regardless of “accepted” reporting limits.For instance, the SWRCB may report estimated values, which can be below reporting limits.
1 Pesticides detected
2 Pesticides detected that are not registered for use in California
37
DPR RESPONSES TO PESTICIDE DETECTIONS
As required under the PCPA (FAC section 13152[e][4]), this section of the annual report describes actions taken by DPR to mitigate the detection of agricultural use pesticides in groundwater (Table 2).
Table 2 summarizes detections of nonpoint agricultural source pesticides in groundwater in 2017 and previously unreported detections by the USGS and DPR’sresponses. Of the 86 agricultural use pesticide/degradate detections reported:
• 15 are pesticides (or degradates of a parent compound) listed under 3CCR section 6800(a) and already regulated as groundwater contaminantswithin GWPAs
• 28 are pesticides (or degradates of a parent compound) listed under 3CCR section 6800(b) as potential groundwater contaminants• 24 are not listed under 3CCR sections 6800(a) or (b); one is a degradate of two parent compounds: one parent is listed under 3CCR section
6800(a) and the second parent is listed under 3CCR section 6800(b)• 18 are no longer registered for use as a pesticide in California (e.g., detections from legacy pesticide use or from non-pesticidal use).
Table 2. Pesticides detected in groundwater in 2017 and previously unreported detections by the USGS. Detection concentrations and drinking water quality standards are reported in parts per billion (ppb). DPR response to agricultural use pesticide detections reported in 2017 and previously unreported detections by the USGS.
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
1,2-Dichloropropane (1,2-D)
(propylene dichloride) 94 45 0.001 – 2.6 5 0.5 5 0 B2 Not registered for use in California
since 1990.
1,4-Dichlorobenzene (p-DCB) 7 2 0.011 - 3.26 5 6 75 75 C
This pesticide is not on the GWPL. ------ This is the first reported detection of this pesticide in California. The two (2) wells with detections over the DPR screening level were determined not to be from legal agricultural use.
38
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
U.S. U.S. OEHHA ††Cancer
CA MCL EPA EPA PHG Group
MCL MCLG
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
2,4-D (2,4-dichlorophenoxy-acetic acid) 1 0 0.03 70 20 70 70 D
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
2,6-Diethylaniline
(degradate of alachlor) 2 0 0.001 - 0.003 --- --- --- --- --- Parent pesticide not registered for use
in California since 2016.
2-Hydroxyatrazine
(degradate of atrazine)1 0 0.003 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). -----No detections were over the DPR screening level.
2-Isopropyl-6-methyl-4-pyrimidinol
(degradate of diazinon)2 1 0.033 - 0.079 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b).----- This is the first reported detection of this pesticide degradate in California. One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
39
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCLOEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
3,4-Dichloroaniline
(degradate of diuron, propanil) 12 1 0.006 - 0.089 --- --- --- --- ---
Parent pesticides are on the GWPL, 3CCR section 6800(a) and (b), respectively. ----- Parent pesticide (believed to be diuron in this instance) is on the GWPL, 3CCR section 6800(a). One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
3,5-Dichloroaniline
(degradate of iprodione, dichloran) 5 0 0.002 - 0.005 --- --- --- --- ---
Parent pesticides are on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
4-Hydroxy chlorothalonil
(degradate of chlorothalonil)1 1 0.088 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b). ----- This is the first reported detection of this pesticide degradate in California. One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
40
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
ACET (deisopropyl-atrazine or deethyl-simazine)
(degradate of atrazine, simazine)
89 75 0.003 - 0.743 --- --- --- --- ---
Parent pesticides are on the GWPL, 3CCR section 6800(a). ----- Sixty-four (64) wells located in Ground Water Protection Areas (GWPAs) had detections that exceeded the DPR
screening level.‡‡ Pesticide applicationsin GWPAs are made under the authority of the Restricted Materials permit program (applications are managed by County Agricultural Commissioners). Eleven (11) wells not in GWPAs had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Acrylonitrile 1 1 0.21 --- --- --- --- B1 Not registered for use in California.
This chemical is also a product of industrial and hazardous waste sites.
Atrazine 104 7 0.001 - 0.6 1 0.15 3 3 N
This pesticide is on the GWPL, 3CCR section 6800(a). ----- One (1) well with a detection over the DPR screening level is in a GWPA. Six (6) wells not in GWPAs had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
41
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Azoxystrobin 1 0 0.002 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Benefin (benfluralin) 3 0 0.002 - 0.003 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Bentazon (Basagran®) 4 0 0.002 - 0.015 18 200 --- --- E
This pesticide is on the GWPL, 3CCR section 6800(a), and listed in 3CCR section 6457. ----- No detections were over the DPR screening level.
Bromacil 31 22 0.001 - 5.48 --- --- --- --- C
This pesticide is on the GWPL, 3CCR section 6800(a). ----- Twenty-one (21) wells with detections over the DPR screening level are in GWPAs. One (1) well not in a GWPA had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
42
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Camphor 2 0 0.021 - 0.035 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Captan 1 1 0.27 --- --- --- --- ---
This pesticide is not on the GWPL. ----- One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Carbon disulfide 53 53 0.1 - 5.2 --- --- --- --- --- Not registered for use in California since 1987.
Chloropicrin 1 0 0.032 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Chlorpyrifos 2 0 0.001 - 0.003 --- --- --- --- D
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
43
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Chlorsulfuron 1 0 0.007 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Chlorthal dimethyl (dacthal/DCPA) 1 0 0.001 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
In March 2018, this pesticide was submitted for evaluation under the formal review process. This decision was based on groundwater detections of the DCPA degradation products (dacthal acid degradates) monomethyl tetrachloroterephthalate (MTP) and 2,3,5,6-tetrachloroterephthalic acid (TPA). DPR completed the formal review process for the dacthal acid degradates and they were found not to pollute at the levels detected.
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
44
DACT (diaminochlorotriazine)
(degradate of simazine) 106 99 0.001 - 5.05 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a).----- Seventy-nine (79) wells with detections over the DPR screening level are in GWPAs. Twenty (20) wells had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Dacthal acid degradates 22 22 0.1 - 1.1 --- --- --- --- ---
This pesticide is not on the GWPL. ----- Twenty-two (22) wells had detections over the DPR screening level. DPR completed the formal review process for dacthal acid degradates in 2018. These degradates were found not to pollute at the levels detected.
Dalapon 1 1 83 200 790 200 200 D Not registered for use in California since 1990.
DBCP (1,2-dibromo-3-chloropropane) 370 239 0.008 - 1.32 0.2 0.0017 0.2 0 B2 Not registered for use in California
since 1990.
45
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
DEA (deethyl-atrazine)
(degradate of atrazine) 101 20 0.002 - 0.276 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). ----- Five (5) wells with detections over the DPR screening level are located in GWPAs. Fifteen (15) wells not in GWPAs had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Dechlorometolachlor
(degradate of metolachlor) 3 0 0.001 - 0.003 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Demethyl fluometuron
(degradate of fluometuron) 2 0 0.001 --- --- --- --- --- Parent pesticide not registered for
in California since 1990. use
Desisopropyl desethyl atrazine
(degradate of atrazine) 3 0 0.001 - 0.011 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). ----- No detections were over the DPR screening level.
Dieldrin 2 1 0.011 - 0.065 --- --- --- --- B2 Not registered for use in California since 1986.
46
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Diflubenzuron 1 0 0.002 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Dimethenamid ESA
(degradate of dimethenamid) 1 0 0.01 --- --- --- --- ---
Dimethenamid-P is on the GWPL, section 6800(b). ----- No detections were over the DPR screening level.
3CCR
Diuron 35 21 0.002 - 0.189 --- --- --- --- L
This pesticide is on the GWPL, 3CCR section 6800(a). ----- Fifteen (15) wells with detections over the DPR screening level are in GWPAs. Six (6) wells not in GWPAs had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Diuron-desmethyl
(degradate of diuron) 23 0 0.001 - 0.023 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). ----- No detections were over the DPR screening level.
47
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
DSMN (desmethyl norflurazon or demethylnorflurazon)
(degradate of norflurazon)
53 32 0.001 - 1.17 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). ----- Thirty-one (31) wells with detections over the DPR screening level are in GWPAs. One (1) well not in a GWPA had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
EPTC (S-ethyl-dipropylthiocarbamate) 3 0 0.007 - 0.015 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Ethylene dibromide (EDB) 9 3 0.008 - 0.17 0.05 0.01⁺⁺ 0.05 0 L Not registered for use in California since 1987.
Ethylene dichloride 3 3 0.09 - 0.26 0.5 0.4 5 0 --- Not registered for use in California since 1987.
Fipronil sulfide
(degradate of fipronil) 5 0 0.003 - 0.007 --- --- --- --- ---
Parent pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
48
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Fipronil sulfonate
(degradate of fipronil) 1 1 0.107 --- --- --- --- ---
Parent pesticide is not on the GWPL. ----- One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Fipronil sulfone
(degradate of fipronil) 1 0 0.003 --- --- --- --- ---
Parent pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Fipronil-carboxamide
(degradate of fipronil) 1 0 0.003 --- --- --- --- ---
Parent pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Fludioxonil 1 1 0.066 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- This is the first reported detection of this pesticide in California. DPR has confirmed the single (1) detection in this well and is conducting further investigation.
Fluometuron 2 0 0.01 --- --- --- --- D Not registered for use in California since 1990.
49
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Glyphosate 1 1 50 700 900 700 700 D
This pesticide is not on the GWPL. ----- The SWRCB resampled the single (1) well with reported detections and found no subsequent residues. DPR will monitor future results from this well before taking further action.
Hexazinone 20 2 0.001 - 0.353 --- --- --- --- D
This pesticide is on the GWPL, 3CCR section 6800(b). ----- DPR completed the formal review process for hexazinone in 2010. These detections were found not to pollute at the levels detected.
Hydroxy monodemethyl fluometuron
(degradate of fluometuron) 1 0 0.009 --- --- --- --- --- Parent pesticide not registered for use in California since 1990.
Hydroxymetolachlor
(degradate of metolachlor) 4 0 0.001 - 0.005 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Hydroxysimazine
(degradate of simazine) 1 0 0.003 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(a). ----- No detections were over the DPR screening level.
50
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Imazaquin 1 0 0.004 --- --- --- --- --- Not registered for use in California.
Detected concentration is below the Reporting Limit.
Imazethapyr 1 0 0.005 --- --- --- --- ---
Imazethapyr ammonium salt is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Imidacloprid 9 7 0.006 - 5.97 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- Two (2) wells had detections reported by USGS that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation. Five (5) wells with detections were sampledby DPR. DPR is expanding sampling forstudy GW17 to include additional areaswith high imidacloprid use and shallowgroundwater.
Linuron 2 0 0.001 - 0.002 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
51
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Malathion 1 0 0.004 --- --- --- --- S
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Methoxyfenozide 16 2 0.001 - 0.286 --- --- --- --- ---
This pesticide is not on the GWPL. ----- This is the first reported detection of this pesticide in California. Two (2) wells had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Methyl iodide 1 1 0.04 --- --- --- --- --- Not registered for use in California since 2012.
Metolachlor 10 1 0.001 - 0.105 --- --- --- --- C
This pesticide is on the GWPL, 3CCR section 6800(b). ----- The single (1) detection over the DPR screening level is in a non-agricultural area, miles from any potential use sites. DPR is contacting USGS for confirmation of this detection. No field investigation is planned.
52
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Metolachlor ESA
(degradate of metolachlor) 13 11 0.004 - 4.37 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b). ----- DPR completed the formal review process for metolachlor degradates in 2016. These degradates were found not to pollute at the levels detected.
Metolachlor OXA
(degradate of metolachlor) 2 2 0.11 - 0.213 --- --- --- --- ---
Parent pesticide is on the GWPL, 3CCR section 6800(b). ----- DPR completed the formal review process for metolachlor degradates in 2016. These degradates were found not to pollute at the levels detected.
Metribuzin 1 0 0.007 --- --- --- --- D
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Molinate 1 0 0.004 20 1 --- --- --- Not registered for use in California since 2009.
Myclobutanil 1 0 0.01 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
53
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Nicosulfuron 1 0 0.001 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Norflurazon 26 16 0.001 - 0.374 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(a). ----- Sixteen (16) wells with detections over the DPR screening level are in GWPAs.
Oryzalin 3 0 0.004 - 0.036 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Oxamyl 1 0 0.001 50 26 200 200 N
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Oxydisulfoton
(degradate of disulfoton) 1 0 0.003 --- --- --- --- --- Parent pesticide not registered for use
in California since 2011.
p-Cresol 3 1 0.01 - 0.08 --- -- --- --- --- Not registered for use in California since 1991.
54
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Pendimethalin 1 0 0.011 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Prometon 24 2 0.002 - 0.151 --- --- --- --- N
This pesticide is on the GWPL, 3CCR section 6800(a). ----- Two (2) wells with detections over the DPR screening level are in GWPAs.
Propanil 2 1 0.005 - 0.06 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- One (1) well had a detection that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Propazine 4 0 0.001 - 0.006 --- --- --- --- N Not registered for use in California since 1988.
Propiconazole 1 0 0.005 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Propoxur 10 0 0.001 - 0.003 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
55
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
Concentration Range (ppb)
†Drinking Water Quality Standards (ppb)
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
CA MCL OEHHA
PHG
U.S.
EPA
MCL
U.S.
EPA
MCLG
††Cancer
Group
Simazine 176 60 0.001 - 0.128 4 4 4 4 N
This pesticide is on the GWPL, 3CCR section 6800(a). ----- Forty-nine (49) wells with detections over the DPR screening level are in GWPAs. Eleven (11) wells had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Sulfentrazone 1 0 0.002 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Sulfometuron methyl 2 0 0.001 - 0.002 --- --- --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Sulfosulfuron 1 0 0.001 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Tebufenozide 1 0 0.001 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
56
Pesticide or
Pesticide Degradate
Wells with
Detections
Wells with Detections
over 0.04 ppb
ConcentrationRange (ppb)
†Drinking Water Quality Standards (ppb)
U.S. U.S. OEHHA ††Canc
CA MCL EPA EPA PHG Group
MCL MCLG
*Groundwater Protection List (GWPL)Status:
3CCR section 6800(a) or (b)
‡DPR Response to Detections(0.04 ppb screening level)
er
Tebuthiuron 18 4 0.002 - 0.121 --- --- --- --- D
This pesticide is on the GWPL, 3CCR section 6800(b). -----Four (4) wells had detections that exeeded the DPR screening level. DPR is currently reviewing these results and is conducting further investigation.
Tetraconazole 3 0 0.001 - 0.037 --- --- --- --- ---
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Thiobencarb 1 0 0.003 70 42 --- --- ---
This pesticide is on the GWPL, 3CCR section 6800(b). ----- No detections were over the DPR screening level.
Trifloxystrobin 1 0 0.001 --- --- --- --- --
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
Trifluralin 4 0 0.001 - 0.006 --- --- --- --- C
This pesticide is not on the GWPL. ----- No detections were over the DPR screening level.
† Drinking water quality standards: MCL: maximum contaminant level; MCLG: maximum contaminant level goal; PHG: public health goal. Other acronyms used include: California(CA); Office of Environmental Health Hazard Assessment (OEHHA); United States Environmental Protection Agency (U.S. EPA).
57
• California (State Water Resources Control Board) MCL values are available at:http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/Documents/DWdocuments/MCLsEPAvsDWP_2018_10_02.pdf.
• Office of Environmental Health Hazard Assessment public health goals available at: https://oehha.ca.gov/water/public-health-goals-phgs.
• U.S. EPA MCL, MCLG, and cancer risk (descriptor) designations derived from the publication 2018 Edition of the Drinking Water Standards and Health Advisories Tablesavailable at: https://www.epa.gov/dwstandardsregulations/2018-drinking-water-standards-and-advisory-tables.
• All health standards not found at sources listed above were derived from the SWRCB water quality goal search app available at:https://www.waterboards.ca.gov/water_issues/programs/water_quality_goals/search.html.
†† Cancer Group (descriptor) acronyms (U.S. EPA): (A) human carcinogen; (B1) probable human carcinogen—indicates limited human evidence; (B2) probable human carcinogen—sufficient evidence in animals and inadequate or no evidence in humans; (C) possible human carcinogen; (D) not classifiable as to human carcinogenicity; (E) evidence of noncarcinogenicity for humans; (L) likely to be carcinogenic to humans; (N) not likely to be carcinogenic in humans; (S) suggestive evidence of carcinogenic potential.
*Pesticides on the Groundwater Protection List (GWPL) 3CCR section 6800(a) or (b) are those labeled for agricultural, outdoor institutional, or outdoor industrial use that havethe potential to pollute groundwater. Section 6800(a) includes seven agricultural herbicides that are regulated as groundwater contaminants: atrazine, bentazon, bromacil,diuron, norflurazon, prometon, and simazine. Section 6800(b) includes 98 pesticides that have the potential to become groundwater contaminants based on their mobility, persistence, and legal uses. The GWPL is available at: http://www.cdpr.ca.gov/docs/legbills/calcode/040101.htm.
If the detected pesticide is regulated as a groundwater contaminant under 3CCR section 6800(a)—and the well is located in a GWPA where use of the pesticide is regulated—current regulation of use is believed to constitute an adequate response to new detections unless concentrations are high enough to indicate existing mitigation measures are not adequate to prevent pollution. (“Pollution” is defined in FAC section 13142 as “…the consequence of polluting,” and “pollute” means “to introduce a pesticide product into the groundwaters of the state resulting in an active ingredient, other specified ingredient, or a degradation product of a pesticide above a level that does not cause adverse health effects, accounting for an adequate margin of safety.”)
‡ DPR responds only to detections of pesticides over the 0.04 ppb screening level unless the drinking water quality standard (health advisory goal/standard) is low. DPR’s policyrelative to its response to reported detections is available at: https://www.cdpr.ca.gov/docs/emon/grndwtr/polprocd/gwp071202.pdf.
‡‡ DPR does not investigate detections within GWPAs for pesticides (or their degradates) that are on the 6800(a) list of known groundwater contaminants (Schuette, 2004). Applications ofthese pesticides in GWPAs are managed by County Agricultural Commissioners via the Restricted Materials permit program. This program requires applicators to modify their pesticide use practices based on soil properties of the GWPA.
⁺⁺ The Public Health Goal (PHG) for ethylene dibromide (EDB) is listed in the SWRCB (not OEHHA) data table under “More about MCLS and PHGs” at the following web address:http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/MCLsandPHGs.shtml. This is a January 10, 2018 update document.
58
REFERENCES
Braun, A. L. and L. S. Hawkins. 1991. Presence of bromacil, diuron, and simazine in surface water runoff from agricultural fields and non-crop site in Tulare County, California.
Clayton, M. 2011. Selection of pesticide active ingredients for future analytical method development and ground water monitoring.
Garretson, C. 1999: Study 182: Protocol for monitoring the concentration of detected pesticides in wells located in highly sensitive areas.
Garretson, C. 2012: Study 182/228 – Preliminary summary of results for well sampling from 1999 through 2011.
Hutson, J.L. 2003. Leaching estimation and chemistry model LEACHM: model description and user’s guide.
Johnson, B. 1991. Setting revised specific numerical values.
Marade, S.J. and J. Troiano. 2000. Sections of land requiring special assignment as runoff or leaching Ground Water Protection Areas.
Schuette, J. 2004. Summary of program policies specifying when the director will not determine if a detection was the result of legal, agricultural use (“N” memorandum). California Department of Pesticide Regulation, Environmental Monitoring Branch. December 1, 2004.
Spurlock, F. 2000. Effect of irrigation scheduling on movement of pesticides to ground water in coarse soils: Monte Carlo analysis of simulation modeling.
Troiano, J., et al. 1993. Influence of amount and method of irrigation water application on leaching of atrazine.
Troiano, J., et al. 1999. Empirical modeling of spatial vulnerability applied to a norflurazon retrospective well study in California. Available at: http://eurekamag.com/research/003/124/003124777.php (verified November 2018).
Troiano, J., et al. 2000. Update of the California vulnerability soil analysis for movement of pesticides to ground water: October 14, 1999.
Troiano, J. and M. Clayton. 2009. Modification of the probabilistic modeling approach to predict well water concentrations used for assessing the risk of ground water contamination by pesticides.